1. Field of the Invention
The present invention is directed to a radio device of the type having an antenna which can be retracted into and withdrawn from a housing.
2. Description of the Prior Art
In given known radio devices or mobile telephone devices (for example, of the type GSM, PCN, PCS, etc.), a combination of an antenna part that is stationary relative to housing of the radio device and a telescoping antenna part is utilized as the antenna. For example, the stationary part is implemented in the form of a helix antenna, whereas the telescoping part is formed by a straight, elongated radiator.
The trend in mobile radiotelephone devices, particularly mobile telephone terminals, is toward smaller and smaller and more and more compact devices. Given extremely small devices, however, a retracted, straight, elongated radiator occupies a relatively large space within the device in relationship to the other components A further reduction in size of such mobile radio devices is precluded by the dimensions of the retractable antennas.
The mechanical length of a radiator given the aforementioned, combined antenna systems is dependent on the frequency to be employed and on the electrical wavelength derived therefrom. In order to achieve an optimal decoupling between the mobile radio device and the antenna in the radio range, the (telescoping) radiator is constructive with a specific length, for example half the electrical wavelength. A mechanically shorter embodiment of the radiator, for example at one-fourth of the electrical wavelength, would in fact be only half as long as the first-cited embodiment of the radiator. Given such a mechanically shortened radiator, however, the radiation behavior would be modified in an undesired way. First, the radiation behavior would be modified by parts of the radio device under the base of the antenna. Second, the radiation behavior also changes in a practically unpredictable way by grasping the device. Given these mechanically shortened radiators, moreover, radio frequency power given transmission events is also emitted beamed,into the body of the user to an extent that may lead to negative effects on health. For these reasons, such shortened radiators do not come into consideration for comprehensive practical use.
These influences can be minimized by a radiator having, for example, xc2xd, xe2x85x9c or ⅝ of the electrical wavelength. However, these advantages are at the expense of larger mechanical length.
It is also known to electrically lengthen mechanically shortened radiators with suitable components at the antenna base in order to obtain a resonant system. For example, an inductance is connected, for example, in series with the radiator. The efficiency of the antenna thereby changes inversely proportionally to the length of the radiator.
In addition to the disadvantage that an additional component is required, another disadvantage is comprised therein that only the shortened radiator contributes to the efficiency of the antenna in such an antenna system. Components at the base of the radiator do not participate in the efficiency and only serve to produce a system capable of resonance.
Given combined antennas that are composed, for example, of a stationary part and a telescoping part, it must also be taken into consideration that an adequate antenna gain must be produced, given an extended antenna compared to the retracted condition, but only the stationary part of the combined antenna is effective for this purpose.
It is an object of the present invention to provide a radio device with an antenna that can be manufactured with relatively small mechanical dimensions and which avoids or minimizes the aforementioned problems associated with known antennas for radio devices.
The above object is achieved in accordance with the principles of the present is invention in a radio device having an antenna which can be retracted into and withdrawn from a housing, and wherein the antenna has the structure of a radiator in the form of a helix.
The invention yields a number of advantages. The inventive radio device has a radiator that exhibits a smaller structural height compared to conventional radiators and that operates without employing an additional component or circuit part for electrical lengthening. The reception or transmission capability of the radiator of the inventive radio device corresponds to that of a conventional radiator.
The radiator of the inventive radio device exhibits the further advantage that the helix can be manufactured in a simple way, requires only relatively little material and thus contributes to a reduction of the weight of the radio device.
The inventive radio device further has the advantage that the emission behavior of the radiator can be adapted to the requirements of the application by forming different pitch angles of the helix. Given an application in the mobile radio field, thus, the RF-irradiation of the body of a user (xe2x80x9cSARxe2x80x9d, specific absorption rate) in transmission mode can be reduced, particularly in the head area.